Hyper-recombination in bacteriophages. As noted above, dam mutants show a high rate of recombination. Since we have recently shown that phage fd DNA and lambda-DNA are devoid of methyladenine in DNA if grown on dam mutants, crosses between various phage mutants will be performed to see if hyper-recombination also occurs with these viruses. Methylation of dam bacterial DNA by phage P1. Phage P1 specifies a DNA adenine methylase which can protect its DNA from degradation by a specific endonuclease. We would like to know if the substrate specificity of the P1 enzyme is the same as the dam enzyme. To test this possibility, P1 lysogens of dam mutants will be constructed and the amount of adenine methylation of bacterial DNA determined. Phenotype of dam recF and dam uvrE bacteria. Bacterial strains mutant in the dam gene and also mutant in the recA or recB,C or polA or lexA genes are inviable. Since recF and uvrF appear to be important in DNA repair we would like to determine if the presence of a dam mutation in such strains also leads to inviability. Purification of the dam adenine methylase. Crude extracts of a mutant strain which has only the dam adenine methylase will be chromatographed on DNA-sepharose and purified. The eluate will be further purified by chromatography on Sephadex-columns. BIBLIOGRAPHIC REFERENCE: Marinus, M.G. (1976) Adenine Methylation of Okazaki Fragments in Escherichia coli. Journal of Bacteriology 128: 853.